what is the difference between application tables and customization tables?

Most of the Tables which are updated using the SPRO config settings are called Customization tables

They start with letter 'T'.

iike--- T001, T002, T003, T005 etc.

Application tables are related the Business transactions in each tables

like in SD SO related table VBAK,VBAP.

and MM related PO tables EKKO, EKPO etc.